The present invention relates to a color mixture prevention technique for an ink-jet printing apparatus that ejects ink droplets of differently colors through a plurality of nozzle opening arrays to provide color printing.
An ink-jet printing apparatus for color printing is so designed that an ink-jet head having a plurality of nozzle opening arrays, generally four or more arrays, through which ink droplets of different colors independently eject is mounted on a carriage. The ink-jet printing apparatus repeats the following processing: while the recording head is moving in the main scanning direction, ink droplets corresponding to print data are ejected, and when the data for one scanning is completed, the print position is shifted a distance equivalent to a predetermined pitch.
Since the color printing quality is greatly affected by the accuracy at which individual dots that constitute pixels are positioned, in the printing apparatus, nozzle openings 2 of each nozzle opening array, through which ink droplets are at least ejected during color printing, are aligned for individual colors along the same scanning lines, as is shown in FIG. 10A, so that a relative accuracy for the positioning of dots that are formed on a recording medium is ensured.
However, since dots of different colors are printed during color printing, the individual ink colors tend to be mixed together.
To resolve this problem, Japanese Unexamined Patent Publication No. Hei 4-118250 proposes a printing method, for an ink-jet printing apparatus, as disclosed in FIG. 10B, whereby nozzle opening arrays C, M, Y and K are shifted so there is one print-pitch between them and so there are four print-pitches between their nozzle openings 2, through which different color ink droplets are ejected, and whereby, during one main scan, to prevent the color-mixing of dots of different- colors are not formed on the same line at the same timing.
However, since during the course of one scan, dots that form one line contact dots in an adjacent line, some color-mixing occurs, and two paper feeding types are required: paper feeding for forming on each print line dots having different colors, and paper feeding by which a printing area is changed by advancing the paper a distance that is equivalent to the printing height of the recording head. Therefore, a paper feeding distance error is varied that cause banding and blank areas, and as a result, an improvement in print quality can not be expected.